It is a goal of those skilled in hot runner design and manufacture, to attempt to configure a hot runner that will deliver a balanced melt flow to the multiple (i.e. plurality) of drops thereof. There are many design, manufacturing, and operational parameters and/or factors that may affect melt flow balance.
One way, at least in theory, to achieve a fully balanced flow to all drops of a hot runner is to make the melt-pressure (i.e. head) loss for all drops substantially identical. Melt-pressure losses in a typical hot runner include those contributed by a sprue, manifold(s), nozzles (including the housing and tip thereof) and mold gates. The melt-pressure losses through the foregoing are effected by a host of factors that include, for example, variations in melt temperature (i.e. effect of viscosity), melt channel diameter, melt channel surface roughness, melt channel length, tip geometry, and gate diameter, gate land, and tip position. With so many variables affecting melt-pressure loss it is little wonder that the prior art attempts at solving this problem have met with limited success or are complex and difficult to implement.
For example, U.S. Pat. No. 5,141,696 issued to Osuna-Diaz on Aug. 25, 1992 describes an engagement for mechanically adjusting the flow through each of a plurality of mold nozzles supplied by a manifold for a multicavity mold, to properly balance the flow into each mold cavity.
U.S. Pat. No. 6,077,470 issued to Beaumont on Jun. 20, 2000 describes a method and apparatus for balancing the filling of injection molds. The apparatus for producing molded products having balanced thermal, material and flow properties includes a device for repositioning a stream of the molten polymer containing material as it flows from a first runner into at least a second downstream runner.
U.S. Pat. No. 6,382,528 issued to Bouti on May 7, 2002 describes an injection molding mixer that reduces the flow imbalances inherent in the melt as the flow branches within a manifold or other part of the injection machine.
U.S. Pat. No. 6,923,638 issued to Chen on Aug. 2, 2005 describes an apparatus for obtaining balanced flow of hot melt in a distribution manifold. In order to achieve more simultaneous delivery, uniform fill rate, and identity of temperature of hot melt across all cavities of a multi-cavity set to achieve more uniform cooling of the preforms, restrictor pin assemblies are provided in association with certain of the branches to adjustably constrict the space available for melt flow from the runner into the branch.
U.S. Pat. No. 7,037,103 issued to Niewels on May 2, 2006 describes an improved injection molding apparatus for a mold using a valve-gated nozzle that includes a receptacle insert with a bore for aligning and sealing with the valve stem.
United States patent publication 2003/0012845 to Doyle et al. published on Jan. 16, 2003 describes an injection molding apparatus that includes an actuator, and a valve pin coupled to the actuator. The valve pin is adapted to open and close a gate of a mold and to control a rate of material flow through the gate during an injection cycle.
United States patent publication 2007/0077328 to Olaru, published on Apr. 2, 2007, describes an injection molding apparatus having a manifold and several manifold melt channels communicating with several hot runner nozzles. A melt redistribution element is placed at specific locations along the melt channels to balance the uneven shear stress profile accumulated during the flow of a melt along the manifold channels.